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 * Copyright (c) 2015, Daniel Murphy, Google
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part of box2d;

/**
 * Implement this class to get contact information. You can use these results for
 * things like sounds and game logic. You can also get contact results by
 * traversing the contact lists after the time step. However, you might miss
 * some contacts because continuous physics leads to sub-stepping.
 * Additionally you may receive multiple callbacks for the same contact in a
 * single time step.
 * You should strive to make your callbacks efficient because there may be
 * many callbacks per time step.
 * @warning You cannot create/destroy Box2D entities inside these callbacks.
 *
 */
abstract class ContactListener {

  /**
   * Called when two fixtures begin to touch.
   * @param contact
   */
  void beginContact(Contact contact);

  /**
   * Called when two fixtures cease to touch.
   * @param contact
   */
  void endContact(Contact contact);

  /**
   * This is called after a contact is updated. This allows you to inspect a
   * contact before it goes to the solver. If you are careful, you can modify the
   * contact manifold (e.g. disable contact).
   * A copy of the old manifold is provided so that you can detect changes.
   * Note: this is called only for awake bodies.
   * Note: this is called even when the number of contact points is zero.
   * Note: this is not called for sensors.
   * Note: if you set the number of contact points to zero, you will not
   * get an EndContact callback. However, you may get a BeginContact callback
   * the next step.
   * Note: the oldManifold parameter is pooled, so it will be the same object for every callback
   * for each thread.
   * @param contact
   * @param oldManifold
   */
  void preSolve(Contact contact, Manifold oldManifold);

  /**
   * This lets you inspect a contact after the solver is finished. This is useful
   * for inspecting impulses.
   * Note: the contact manifold does not include time of impact impulses, which can be
   * arbitrarily large if the sub-step is small. Hence the impulse is provided explicitly
   * in a separate data structure.
   * Note: this is only called for contacts that are touching, solid, and awake.
   * @param contact
   * @param impulse this is usually a pooled variable, so it will be modified after
   * this call
   */
  void postSolve(Contact contact, ContactImpulse impulse);
}
